The present invention relates to an air-condition controlling apparatus for automobiles for automatically changing the air conditioning state between internal air circulation and intake of outdoor air in an air conditioner.
It has been well known from Japanese Patent Publication No. 47-36974, that a conventional control unit includes an air conditioning unit in which the upstream side is selectively connected to the outside of the automobile and the downstream side is connected to the inside of the automobile, an operating unit for selecting the intake of air from the outside of the automobile and from the inside of the automobile within the air conditioning unit, and a detector for generating an electrical signal in accordance with impurity components included in the outside air of the automobile, said operating unit being set by a controller to a state of internal air circulation (the state of taking in air from inside the automobile) in accordance with the electrical signal of said detector.
However, the well-known prior art makes clear only the fact that the state of air intake from the outside of the automobile is changed over to the state of internal air circulation when the electrical signal of said detector shows a larger value than a predetermined value. In order to achieve more desirable practical applications, however, detection must be carried out by taking into consideration temperature and humidity characteristics of said detector and time change, etc.
When a gas detector is to be used as a detecting means, a gas detector of solid heat conduction type can be considered proper for use in an automobile, upon considering structure, price, etc. among various types of gas detectors to which a semi-conductor and other systems are applied. A gas detector of this type utilizes such an operating principle that when a metal oxide semiconductor such as SnO.sub.2 or the like is heated within the range of about 300.degree. C. to 500.degree. C. so that inflammable gas is absorbed in the semiconductor, the thermal conductivity of the semiconductor becomes larger to improve heat discharge thereby lowering the temperature of the semiconductor and reducing the resistance of a platinum wire for heating the semiconductor.
The present inventors carried out an experiment to check to see to what extent a deviation voltage would occur at a gas detector forming one leg of a bridge circuit when an automobile is run in a town with said gas detector disposed at an outdoor air inlet path in order to detect the degree of impurity of air outside the automobile. As a result of this experiment, the size of deviation voltage was very small with approximately 50 mV as a maximum, although the value may depend on the area in which the automobile runs. On the other hand, when the humidity characteristics of said gas detector changed from the absolute humidity of 1 g/m.sup.3 to 100 g/m.sup.3, deviation voltage was as high as approximately 50 mV, and further the voltage change of approximately 10 mV was observed due to the change of time. It was made clear that this detector cannot be expected to carry out desirable operation as a control unit according to the simple detection method as shown in said prior art.